U.S. patent application number 13/770590 was filed with the patent office on 2013-10-17 for hierarchical channel sounding and channel state information feedback in massive mimo systems.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. The applicant listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Kaushik Josiam, Ying Li, Zhouyue Pi.
Application Number | 20130272263 13/770590 |
Document ID | / |
Family ID | 49325008 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130272263 |
Kind Code |
A1 |
Pi; Zhouyue ; et
al. |
October 17, 2013 |
HIERARCHICAL CHANNEL SOUNDING AND CHANNEL STATE INFORMATION
FEEDBACK IN MASSIVE MIMO SYSTEMS
Abstract
Time, frequency and spatial processing parameters for
communications between a base station and a mobile station are
selected by transmitting synchronization signals in multiple slices
of a wireless transmission sector for the base station, and
receiving feedback from the mobile station of at least one
preferred slice of the multiple slices. In response to selection of
one of the slices as an active slice for communications between the
base station and the mobile station, reference signals are
transmitted in the selected active slice using a corresponding
selected precoder and/or codebook. The mobile station estimates and
feeds back channel state information (CSI) based on those reference
signals, and the CSI is then employed to determine communication
parameters for communications between the base station and mobile
station that are specific to the mobile station.
Inventors: |
Pi; Zhouyue; (Allen, TX)
; Li; Ying; (Garland, TX) ; Josiam; Kaushik;
(Dallas, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Suwon-si |
|
KR |
|
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
49325008 |
Appl. No.: |
13/770590 |
Filed: |
February 19, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61624841 |
Apr 16, 2012 |
|
|
|
Current U.S.
Class: |
370/330 |
Current CPC
Class: |
H04L 5/0023 20130101;
H04L 25/0204 20130101; H04L 25/0226 20130101; H04L 5/0048 20130101;
H04B 7/0626 20130101; H04L 1/0026 20130101; H04W 72/042 20130101;
H04L 5/0057 20130101 |
Class at
Publication: |
370/330 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Claims
1. A method, comprising: transmitting a plurality of
synchronization signals each using a different transmitter spatial
processing scheme and one or more sector-level reference signals
from a base station to at least one mobile station within a sector;
based upon long-term channel state information (CSI) determined
using the synchronization signals and the sector-level reference
signals, transmitting one or more selected slice-level reference
signals to the at least one MS; and based upon short-term CSI
determined using the selected slice-level reference signals,
selecting time, frequency and spatial processing schemes for at
least some subsequent communications between the base station and
the mobile station.
2. The method according to claim 1, wherein the long-term CSI
comprises one or more of a number of communication paths between
the base station and the mobile station, and angle of departure and
angle of arrival pairs for communication paths between the base
station and the mobile station.
3. The method according to claim 1, wherein the short-term CSI
comprises complex channel coefficients.
4. The method according to claim 1, wherein the synchronization
signals comprise a sequence of synchronization signals selected
based upon a cell index, a time index, a frequency index and a
spatial index, mapped to time-frequency resources according to the
time and frequency indices, and spatially processed according to
the spatial index.
5. The method according to claim 1, wherein the synchronization
signals are transmitted using at least one of different beamforming
(BF), space division multiple access (SDMA), or multiple input,
multiple output (MIMO) transmitter codebooks and different BF,
SDMA, or MIMO transmitter precoders.
6. The method according to claim 1, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises selecting one of a plurality of
transmitter spatial processing schemes.
7. The method according to claim 6, wherein selecting one of a
plurality of transmitter spatial processing schemes comprises
either selecting one of a plurality of different beamforming (BF),
space division multiple access (SDMA), or multiple input, multiple
output (MIMO) transmitter codebooks, or selecting one of a
plurality of different BF, SDMA, or MIMO transmitter precoders.
8. The method according to claim 7, wherein selection of one of a
plurality of different BF, SDMA, or MIMO transmitter precoders is
based upon an index of a mobile station feedback field.
9. The method according to claim 1, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises selecting one of a plurality of receiver
spatial processing schemes.
10. The method according to claim 9, wherein selecting one of a
plurality of receiver spatial processing schemes comprises either
selecting one of a plurality of different beamforming (BF), space
division multiple access (SDMA), or multiple input, multiple output
(MIMO) receiver codebooks, or selecting one of a plurality of
different BF, SDMA, or MIMO receiver precoders.
11. The method according to claim 10, wherein selection of one of a
plurality of different BF, SDMA, or MIMO receiver precoders is
based upon an index of a mobile station feedback field.
12. The method according to claim 1, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: multiplexing slice-level common reference
signals (CRSs) of different slices in same time and frequency
resources.
13. The method according to claim 1, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: dynamically adjusting a configuration of
slice-level common reference signals (CRSs) by one of turning on or
off slice-level CRSs within one of the slices and configuring a
density of slice-level CRSs within one of the slices; and upon
adjusting the configuration of slice-level CRSs, signaling changes
to the mobile station.
14. The method according to claim 1, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: using a transmitter beamforming precoder
having strong spatial correlation to a slice in which the mobile
station is located.
15. The method according to claim 1, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: multiplexing slice-level channel state
information reference signals (CSI-RSs) of different slices in same
time and frequency resources.
16. The method according to claim 1, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: dynamically adjusting a configuration of
slice-level channel state information reference signals (CSI-RSs)
by one of turning on or off slice-level CSI-RSs within one of the
slices and configuring a density of slice-level CSI-RSs within one
of the slices; and upon adjusting the configuration of slice-level
CSI-RSs, signaling changes to the mobile station.
17. A method, comprising: transmitting a plurality of
synchronization signals each using a different transmitter spatial
processing scheme and one or more sector-level reference signals
from a base station to at least one mobile station within a sector;
based upon long-term channel state information (CSI) determined
using the synchronization signals and the sector-level reference
signals, transmitting slice-level reference signals within one or
more selected slices in the sector to the at least one MS; and
based upon short-term CSI determined using the selected slice-level
reference signals, selecting time, frequency and spatial processing
schemes for at least some subsequent communications between the
base station and the mobile station.
18. The method according to claim 17, wherein the long-term CSI
comprises one or more of a number of communication paths between
the base station and the mobile station, and angle of departure and
angle of arrival pairs for communication paths between the base
station and the mobile station.
19. The method according to claim 17, wherein the short-term CSI
comprises complex channel coefficients.
20. The method according to claim 17, wherein the synchronization
signals comprise a sequence of synchronization signals selected
based upon a cell index, a time index, a frequency index and a
spatial index, mapped to time-frequency resources according to the
time and frequency indices, and spatially processed according to
the spatial index.
21. The method according to claim 17, wherein the synchronization
signals are transmitted using at least one of different beamforming
(BF), space division multiple access (SDMA), or multiple input,
multiple output (MIMO) transmitter codebooks and different BF,
SDMA, or MIMO transmitter precoders.
22. The method according to claim 17, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises selecting one of a plurality of
transmitter spatial processing schemes.
23. The method according to claim 22, wherein selecting one of a
plurality of transmitter spatial processing schemes comprises
either selecting one of a plurality of different beamforming (BF),
space division multiple access (SDMA), or multiple input, multiple
output (MIMO) transmitter codebooks, or selecting one of a
plurality of different BF, SDMA, or MIMO transmitter precoders.
24. The method according to claim 23, wherein selection of one of a
plurality of different BF, SDMA, or MIMO transmitter precoders is
based upon an index of a mobile station feedback field.
25. The method according to claim 17, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises selecting one of a plurality of receiver
spatial processing schemes.
26. The method according to claim 25, wherein selecting one of a
plurality of receiver spatial processing schemes comprises either
selecting one of a plurality of different beamforming (BF), space
division multiple access (SDMA), or multiple input, multiple output
(MIMO) receiver codebooks, or selecting one of a plurality of
different BF, SDMA, or MIMO receiver precoders.
27. The method according to claim 26, wherein selection of one of a
plurality of different BF, SDMA, or MIMO receiver precoders is
based upon an index of a mobile station feedback field.
28. The method according to claim 17, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: multiplexing slice-level common reference
signals (CRSs) of different slices in same time and frequency
resources.
29. The method according to claim 17, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: dynamically adjusting a configuration of
slice-level common reference signals (CRSs) by one of turning on or
off slice-level CRSs within one of the slices and configuring a
density of slice-level CRSs within one of the slices; and upon
adjusting the configuration of slice-level CRSs, signaling changes
to the mobile station.
30. The method according to claim 17, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: using a transmitter beamforming precoder
having strong spatial correlation to a slice in which the mobile
station is located.
31. The method according to claim 17, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: multiplexing slice-level channel state
information reference signals (CSI-RSs) of different slices in same
time and frequency resources.
32. The method according to claim 17, wherein transmitting one or
more selected slice-level reference signals to the at least one
mobile station comprises: dynamically adjusting a configuration of
slice-level channel state information reference signals (CSI-RSs)
by one of turning on or off slice-level CSI-RSs within one of the
slices and configuring a density of slice-level CSI-RSs within one
of the slices; and upon adjusting the configuration of slice-level
CSI-RSs, signaling changes to the mobile station.
33. A base station, comprising: a transmitter configured to
transmit a plurality of synchronization signals each using a
different transmitter spatial processing scheme and one or more
sector-level reference signals from the base station to at least
one mobile station within a sector, wherein, based upon long-term
channel state information (CSI) determined using the
synchronization signals and the sector-level reference signals, the
transmitter is configured to transmit one or more selected
slice-level reference signals to the at least one MS; and a
controller configured, based upon short-term CSI determined using
the selected slice-level reference signals, to select time,
frequency and spatial processing schemes for at least some
subsequent communications between the base station and the mobile
station.
34. The base station according to claim 33, wherein the long-term
CSI comprises one or more of a number of communication paths
between the base station and the mobile station, and angle of
departure and angle of arrival pairs for communication paths
between the base station and the mobile station.
35. The base station according to claim 33, wherein the short-term
CSI comprises complex channel coefficients.
36. The base station according to claim 33, wherein the
synchronization signals comprise a sequence of synchronization
signals selected based upon a cell index, a time index, a frequency
index and a spatial index, mapped to time-frequency resources
according to the time and frequency indices, and spatially
processed according to the spatial index.
37. The base station according to claim 33, wherein the
synchronization signals are transmitted using at least one of
different beamforming (BF), space division multiple access (SDMA),
or multiple input, multiple output (MIMO) transmitter codebooks and
different BF, SDMA, or MIMO transmitter precoders.
38. The base station according to claim 33, wherein the controller
is configured to select one of a plurality of transmitter spatial
processing schemes to transmit the one or more selected slice-level
reference signals to the at least one mobile station comprises.
39. The base station according to claim 38, wherein the controller
is configured to either select one of a plurality of different
beamforming (BF), space division multiple access (SDMA), or
multiple input, multiple output (MIMO) transmitter codebooks, or
select one of a plurality of different BF, SDMA, or MIMO
transmitter precoders.
40. The base station according to claim 39, wherein the controller
is configured to select one of a plurality of different BF, SDMA,
or MIMO transmitter precoders based upon an index of a mobile
station feedback field.
41. The base station according to claim 33, wherein the controller
is configured to select one of a plurality of receiver spatial
processing schemes.
42. The base station according to claim 41, wherein the controller
is configured to either select one of a plurality of different
beamforming (BF), space division multiple access (SDMA), or
multiple input, multiple output (MIMO) receiver codebooks, or
select one of a plurality of different BF, SDMA, or MIMO receiver
precoders.
43. The base station according to claim 33, wherein the controller
is configured to selected one of a plurality of different BF, SDMA,
or MIMO receiver precoders based upon an index of a mobile station
feedback field.
44. The base station according to claim 33, wherein the controller
is configured to multiplex slice-level common reference signals
(CRSs) of different slices in same time and frequency
resources.
45. The base station according to claim 33, wherein the controller
is configured to dynamically adjust a configuration of slice-level
common reference signals (CRSs) by one of turning on or off
slice-level CRSs within one of the slices and configuring a density
of slice-level CRSs within one of the slices, and upon adjusting
the configuration of slice-level CRSs, signal changes to the mobile
station.
46. The base station according to claim 33, wherein the controller
is configured to use a transmitter beamforming precoder having
strong spatial correlation to a slice in which the mobile station
is located.
47. The base station according to claim 33, wherein the controller
is configured to multiplex slice-level channel state information
reference signals (CSI-RSs) of different slices in same time and
frequency resources.
48. The base station according to claim 33, wherein the controller
is configured to dynamically adjust a configuration of slice-level
channel state information reference signals (CSI-RSs) by one of
turning on or off slice-level CSI-RSs within one of the slices and
configuring a density of slice-level CSI-RSs within one of the
slices, and upon adjusting the configuration of slice-level
CSI-RSs, signal changes to the mobile station.
49. A base station, comprising: a transmitter configured to
transmit a plurality of synchronization signals each using a
different transmitter spatial processing scheme and one or more
sector-level reference signals from the base station to at least
one mobile station within a sector, wherein, based upon long-term
channel state information (CSI) determined using the
synchronization signals and the sector-level reference signals, the
transmitter is configured to transmit slice-level reference signals
within one or more selected slices in the sector to the at least
one MS; and a controller configured, based upon short-term CSI
determined using the selected slice-level reference signals, to
select time, frequency and spatial processing schemes for at least
some subsequent communications between the base station and the
mobile station.
50. The base station according to claim 49, wherein the long-term
CSI comprises one or more of a number of communication paths
between the base station and the mobile station, and angle of
departure and angle of arrival pairs for communication paths
between the base station and the mobile station.
51. The base station according to claim 49, wherein the short-term
CSI comprises complex channel coefficients.
52. The base station according to claim 49, wherein the
synchronization signals comprise a sequence of synchronization
signals selected based upon a cell index, a time index, a frequency
index and a spatial index, mapped to time-frequency resources
according to the time and frequency indices, and spatially
processed according to the spatial index.
53. The base station according to claim 49, wherein the
synchronization signals are transmitted using at least one of
different beamforming (BF), space division multiple access (SDMA),
or multiple input, multiple output (MIMO) transmitter codebooks and
different BF, SDMA, or MIMO transmitter precoders.
54. The base station according to claim 49, wherein the controller
is configured to select one of a plurality of transmitter spatial
processing schemes to transmit the one or more selected slice-level
reference signals to the at least one mobile station comprises.
55. The base station according to claim 54, wherein the controller
is configured to either select one of a plurality of different
beamforming (BF), space division multiple access (SDMA), or
multiple input, multiple output (MIMO) transmitter codebooks, or
select one of a plurality of different BF, SDMA, or MIMO
transmitter precoders.
56. The base station according to claim 55, wherein the controller
is configured to select one of a plurality of different BF, SDMA,
or MIMO transmitter precoders based upon an index of a mobile
station feedback field.
57. The base station according to claim 49, wherein the controller
is configured to select one of a plurality of receiver spatial
processing schemes.
58. The base station according to claim 57, wherein the controller
is configured to either select one of a plurality of different
beamforming (BF), space division multiple access (SDMA), or
multiple input, multiple output (MIMO) receiver codebooks, or
select one of a plurality of different BF, SDMA, or MIMO receiver
precoders.
59. The base station according to claim 49, wherein the controller
is configured to selected one of a plurality of different BF, SDMA,
or MIMO receiver precoders based upon an index of a mobile station
feedback field.
60. The base station according to claim 49, wherein the controller
is configured to multiplex slice-level common reference signals
(CRSs) of different slices in same time and frequency
resources.
61. The base station according to claim 49, wherein the controller
is configured to dynamically adjust a configuration of slice-level
common reference signals (CRSs) by one of turning on or off
slice-level CRSs within one of the slices and configuring a density
of slice-level CRSs within one of the slices, and upon adjusting
the configuration of slice-level CRSs, signal changes to the mobile
station.
62. The base station according to claim 49, wherein the controller
is configured to use a transmitter beamforming precoder having
strong spatial correlation to a slice in which the mobile station
is located.
63. The base station according to claim 49, wherein the controller
is configured to multiplex slice-level channel state information
reference signals (CSI-RSs) of different slices in same time and
frequency resources.
64. The base station according to claim 49, wherein the controller
is configured to dynamically adjust a configuration of slice-level
channel state information reference signals (CSI-RSs) by one of
turning on or off slice-level CSI-RSs within one of the slices and
configuring a density of slice-level CSI-RSs within one of the
slices, and upon adjusting the configuration of slice-level
CSI-RSs, signal changes to the mobile station.
65. A method, comprising: receiving, at a mobile station within a
sector served by at least one base station, at least one of a
plurality of synchronization signals each using a different
transmitter spatial processing scheme and one or more sector-level
reference signals from the at least one base station; determining
long-term channel state information (CSI) using the synchronization
signals and the sector-level reference signals; based on the
long-term CSI, determining one or more preferred slices in the
sector for communications between the at least one base station and
the mobile station; and transmitting a signal indicating the one or
more preferred slices to the at least one base station.
66. The method according to claim 65, wherein the long-term CSI
comprises one or more of a number of communication paths between
the base station and the mobile station, and angle of departure and
angle of arrival pairs for communication paths between the base
station and the mobile station.
67. The method according to claim 65, further comprising:
receiving, at the mobile station from the at least one base
station, one or more slice-level reference signals; determining
short-term CSI; and signaling information based on the short-term
CSI to the at least one base station.
68. The method according to claim 67, wherein the short-term CSI
comprises complex channel coefficients.
69. The method according to claim 67, wherein the signal indicating
the one or more preferred slices corresponds to at least one of
different beamforming (BF), space division multiple access (SDMA),
or multiple input, multiple output (MIMO) transmitter codebooks and
different BF, SDMA, or MIMO transmitter precoders.
70. The method according to claim 67, wherein the one or more
slice-level reference signals are transmitted using one of a
plurality of transmitter spatial processing schemes.
71. The method according to claim 67, further comprising:
transmitting a mobile station feedback field corresponding to one
of a plurality of different BF, SDMA, or MIMO transmitter
precoders.
72. The method according to claim 65, further comprising: using a
selected one of a plurality of receiver spatial processing
schemes.
73. A mobile station, comprising: a receiver configured to receive,
at the mobile station within a sector served by at least one base
station, at least one of a plurality of synchronization signals
each using a different transmitter spatial processing scheme and
one or more sector-level reference signals from the at least one
base station; a controller configured to determine long-term
channel state information (CSI) using the synchronization signals
and the sector-level reference signals, and, based on the long-term
CSI, to determine one or more preferred slices in the sector for
communications between the at least one base station and the mobile
station; and a transmitter configured to transmit a signal
indicating the one or more preferred slices to the at least one
base station.
74. The mobile station according to claim 73, wherein the long-term
CSI comprises one or more of a number of communication paths
between the base station and the mobile station, and angle of
departure and angle of arrival pairs for communication paths
between the base station and the mobile station.
75. The mobile station according to claim 73, wherein the receiver
is configured to receive, at the mobile station from the at least
one base station, one or more slice-level reference signals,
wherein the controller is configured to determine short-term CSI,
and wherein the transmitter is configured to signal information
based on the short-term CSI to the at least one base station.
76. The mobile station according to claim 75, wherein the
short-term CSI comprises complex channel coefficients.
77. The mobile station according to claim 75, wherein the signal
indicating the one or more preferred slices corresponds to at least
one of different beamforming (BF), space division multiple access
(SDMA), or multiple input, multiple output (MIMO) transmitter
codebooks and different BF, SDMA, or MIMO transmitter
precoders.
78. The mobile station according to claim 75, wherein the one or
more slice-level reference signals are transmitted using one of a
plurality of transmitter spatial processing schemes.
79. The mobile station according to claim 75, wherein the
transmitter is configured to transmit a mobile station feedback
field corresponding to one of a plurality of different BF, SDMA, or
MIMO transmitter precoders.
80. The mobile station according to claim 73, wherein receiver is
configured to use a selected one of a plurality of receiver spatial
processing schemes.
Description
[0001] This application hereby incorporates by reference U.S.
Provisional Patent Application Ser. No. 61/624,841, filed Apr. 16,
2012, entitled "HIERARCHICAL CHANNEL SOUNDING AND CHANNEL STATE
INFORMATION FEEDBACK IN MASSIVE MIMO SYSTEMS."
TECHNICAL FIELD
[0002] The present disclosure relates generally to channel state
information feedback in wireless mobile communication systems and,
more specifically, to hierarchical channel sounding and channel
state information feedback in massive multiple input, multiple
output (MIMO) wireless communication systems.
BACKGROUND
[0003] One of the key challenges for improving the capacity of
wireless communications systems with large numbers of transmitter
and/or receiver antennae is the large amount of channel state
information that must be acquired. For example, with a 256-element
base station antenna array and a 64-element mobile station antenna
array, the channel matrix between the two devices has a dimension
of 256.times.64, which would be practically impossible to estimate
if channel estimation were performed on a per element basis.
[0004] There is, therefore, a need in the art to develop improved
techniques for acquiring channel state information in massive MIMO
systems with large numbers of transmitter and receiver
antennas.
SUMMARY
[0005] Time, frequency and spatial processing parameters for
communications between a base station and a mobile station are
selected by transmitting synchronization signals in multiple slices
of a wireless transmission sector for the base station, and
receiving feedback from the mobile station of at least one
preferred slice of the multiple slices. In response to selection of
one of the slices as an active slice for communications between the
base station and the mobile station, reference signals are
transmitted in the selected active slice using a corresponding
selected precoder and/or codebook. The mobile station estimates and
feeds back channel state information (CSI) based on those reference
signals, and the CSI is then employed to determine communication
parameters for communications between the base station and mobile
station that are specific to the mobile station.
[0006] Before undertaking the DETAILED DESCRIPTION below, it may be
advantageous to set forth definitions of certain words and phrases
used throughout this patent document: the terms "include" and
"comprise," as well as derivatives thereof, mean inclusion without
limitation; the term "or," is inclusive, meaning and/or; the
phrases "associated with" and "associated therewith," as well as
derivatives thereof, may mean to include, be included within,
interconnect with, contain, be contained within, connect to or
with, couple to or with, be communicable with, cooperate with,
interleave, juxtapose, be proximate to, be bound to or with, have,
have a property of, or the like; and the term "controller" means
any device, system or part thereof that controls at least one
operation, where such a device, system or part may be implemented
in hardware that is programmable by firmware or software. It should
be noted that the functionality associated with any particular
controller may be centralized or distributed, whether locally or
remotely. Definitions for certain words and phrases are provided
throughout this patent document, those of ordinary skill in the art
should understand that in many, if not most instances, such
definitions apply to prior, as well as future uses of such defined
words and phrases.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] For a more complete understanding of the present disclosure
and its advantages, reference is now made to the following
description taken in conjunction with the accompanying drawings, in
which like reference numerals represent like parts:
[0008] FIG. 1 is a high level diagram illustrating an exemplary
massive MIMO wireless network implementing hierarchical channel
sounding and channel state information feedback according to one or
more embodiments of the present disclosure;
[0009] FIG. 1A is a high level block diagram illustrating further
details relating to components within the massive MIMO wireless
communication system of FIG. 1;
[0010] FIG. 2 diagrammatically illustrates some spatial processing
technologies that may be employed during hierarchical channel
sounding and channel state information feedback within a massive
MIMO wireless network according to one or more embodiments of the
present disclosure;
[0011] FIG. 3 illustrates a timing for hierarchical channel
sounding and channel state information feedback within a massive
MIMO wireless network according to one embodiment of the present
disclosure;
[0012] FIGS. 4A and 4B illustrate time-frequency-space multiplexing
of synchronization signals in connection with hierarchical channel
sounding and channel state information feedback within a massive
MIMO wireless network according to one embodiment of the present
disclosure;
[0013] FIG. 5 illustrates one example of the BS and MS operation
for acquiring long-term large-scale channel state information via
sync signals according to one embodiment of the present
disclosure;
[0014] FIG. 6 is a process flow diagram of an example of base
station and mobile station operation with short-term CSI feedback
depending on long-term CSI feedback according to one embodiment of
the present disclosure;
[0015] FIG. 7 is a process flow diagram of an example of channel
sounding and CSI feedback with configurable slice-level CSI-RS (or
CRS) according to one embodiment of the present disclosure;
[0016] FIG. 8 is an example of slice-level CSI-RS transmission for
use in channel sounding and CSI feedback with configurable
slice-level CSI-RS (or CRS) according to one embodiment of the
present disclosure;
[0017] FIG. 9 is a process flow diagram for one example of
MS-specific CSI-RS transmission and the associated CSI feedback
according to one embodiment of the present disclosure;
[0018] FIG. 10 is a process flow diagram for another example of
MS-specific CSI-RS transmission and the associated CSI feedback
according to one embodiment of the present disclosure;
[0019] FIG. 11 is an alternative illustration of the hierarchical
CSI acquisition depicted in FIG. 3;
[0020] FIG. 12 depicts one example of a simplified hierarchical
channel sounding and CSI estimation scheme according to one
embodiment of the present disclosure;
[0021] FIG. 13 depicts an example of hierarchical uplink channel
sounding and CSI estimation according to one embodiment of the
present disclosure; and
[0022] FIG. 14 depicts another example of a hierarchical uplink CSI
acquisition scheme according to one embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0023] FIGS. 1 through 14, discussed below, and the various
embodiments used to describe the principles of the present
disclosure in this patent document are by way of illustration only
and should not be construed in any way to limit the scope of the
disclosure. Those skilled in the art will understand that the
principles of the present disclosure may be implemented in any
suitably arranged wireless communication system.
[0024] To satisfy the explosive growth of mobile (wireless)
broadband data traffic, next generation wireless communication
systems (i.e., 5.sup.th Generation or "5G") need to provide 100 to
1,000 times more capacity than existing 4.sup.th Generation (4G)
systems such as Long Term Evolution (LTE), LTE-Advanced, mobile
Worldwide Interoperability for Microwave Access (WiMAX) Evolution,
etc. Two technologies projected to provide the needed magnitude of
capacity improvement are massive MIMO transmission and exploitation
of millimeter (mm) wavelength (mm-wave) mobile broadband
frequencies (e.g., wavelengths of between 1 mm and 100 mm,
corresponding to frequencies of between 3 and 300 gigaHertz (GHz)).
The former is described in T. L. Marzetta, "Non-cooperative
Cellular Wireless with Unlimited Number of Base Station Antennas,"
IEEE Trans. Wireless Communication, vol. 9, no. 11, pp. 3590-3600,
November 2010, and the latter in Zhouyue Pi & Farooq Khan, "An
Introduction to Millimeter-Wave Mobile Broadband Systems," IEEE
Communications Magazine, June 2011, each of which is incorporated
herein by reference. These two technologies are complementary since
higher communication frequencies allow for smaller antennas in base
stations and mobile stations, which in turn allow greater numbers
of antennas in the same area. For example, for a mm-wave mobile
communication system deployed in 6 GHz, the wavelength is 5
centimeters (cm) and the size of a half-wavelength dipole antenna
is 2.5 cm, making possible a 256-element antenna array at the base
station with the total array size less than 40 cm.times.40 cm and a
16-element antenna array at the mobile station with a total array
size of less than 10 cm.times.10 cm. Further up the spectrum, it
becomes possible to put thousands of antennas in a base station and
hundreds of antennas in a mobile station, all in practical form
factors for mobile communication devices.
[0025] Spatial signal processing technologies with large numbers of
antennas, including beamforming (BF), spatial division multiple
access (SDMA), and massive MIMO are key to enabling mm-wave mobile
broadband communication and drastic performance improvements beyond
4G. With large numbers of antennas at base stations and mobile
stations, significant transmitter and receiver BF gain can be
achieved, overcoming the path loss disadvantage of high frequency
propagation and suppressing unwanted interference. Transmitter and
receiver BF with large numbers of antennas can achieve wide area
coverage and high spectral efficiency for mm-wave mobile
communication, with good spatial separation achieved between links
from the same base station to different mobile stations in the
downlink, and between links from different mobile stations to the
same base station in the uplink. Such spatial separation allows a
large degree of freedom in SDMA, which in turn significantly
improves system capacity. When the communication channel between a
base station and a mobile station becomes sufficiently scattered, a
large degree of freedom can also be achieved on the point-to-point
communications between the base station and the mobile station, in
which case MIMO communication with large rank can be achieved to
significantly boost the spectral efficiency for the point-to-point
communication links.
[0026] As noted above, one of the key challenges for efficient
implementation of BF/SDMA/MIMO with large numbers of transmitter
and/or receiver antennas is the large amount of channel state
information that must be acquired. In accordance with the present
disclosure, channel sounding signals (or reference signals) are
transmitted and channel state information is estimated and reported
in massive MIMO systems with large number of antennas.
[0027] As used herein, BF, SDMA, and MIMO are generally referred to
collectively as members of the category "spatial processing." For
the purpose of illustration, many embodiments are described using
transmitter (Tx) and receiver (Rx) BF as examples. However, those
embodiments are equally applicable to cases where SDMA and/or MIMO
are used (or also used) as spatial processing techniques.
[0028] FIG. 1 is a high level diagram illustrating an exemplary
massive MIMO wireless network implementing hierarchical channel
sounding and channel state information feedback according to one or
more embodiments of the present disclosure. The wireless network
100 illustrated in FIG. 1 is provided solely for purposes of
explaining the subject matter of the present disclosure, and is not
intended to suggest any limitation regarding the applicability of
that subject matter. Other wireless networks may employ the subject
matter depicted in the drawings and described herein without
departing from the scope of the present disclosure. In addition,
those skilled in the art will recognize that the complete structure
and operation of a wireless network and the components thereof are
depicted in the drawings and described therein. Instead, for
simplicity and clarity, only so much of the structure and operation
of the wireless network and the components thereof as are unique to
the present disclosure or necessary for an understanding of the
present disclosure are depicted and described.
[0029] In the illustrated embodiment, wireless network 100 includes
a base station (BS) 101, BS 102, and BS 103. Depending on the
network type, other well-known terms may be used instead of "base
station," such as "Evolved Node B" (eNB) or "access point" (AP).
For simplicity and clarity, the term "base station" will be used
herein to refer to the network infrastructure components that
provide wireless access to remote (mobile or fixed) terminals.
[0030] The BS 101 communicates with BS 102 and BS 103 via network
130 operating according to a standardized protocol (e.g., X2
protocol), via a proprietary protocol, or preferably via Internet
protocol (IP). IP network 130 may include any IP-based network or a
combination thereof, such as the Internet, a proprietary IP
network, or another data network.
[0031] The BS 102 provides wireless broadband access to a first
plurality of mobile stations (MSs) within coverage area 120 of BS
102. In the example illustrated, the first plurality of MSs
includes MS 111, which may be located in a small business; MS 112,
which may be located in an enterprise; MS 113, which may be located
in a WiFi hotspot; MS 114, which may be located in a first
residence; MS 115, which may be located in a second residence; and
MS 116, which may be a mobile device, such as a cell phone, a
wireless laptop, a wireless-enabled tablet, or the like. For
simplicity and clarity, the term "mobile station" or "MS" is used
herein to designate any remote wireless equipment that wirelessly
accesses or communicates with a BS, whether the MS is a mobile
device (e.g., cell phone, wireless-enabled tablet or laptop, etc.)
or is normally considered a stationary device (e.g., desktop
personal computer, wireless television receiver, etc.). In other
systems, other well-known terms may be used instead of "mobile
station," such as "user equipment" (UE), "subscriber station" (SS),
"remote terminal" (RT), "wireless terminal" (WT), and the like.
[0032] The BS 103 provides wireless broadband access to a second
plurality of MSs within coverage area 125 of BS 103. The second
plurality of MSs includes MS 115 and MS 116. In an exemplary
embodiment, BSs 101-103 communicate with each other and with MSs
111-116 using millimeter wave wireless communications. While only
six MSs are depicted in FIG. 1, it will be understood that wireless
network 100 may provide wireless broadband access to additional
MSs.
[0033] FIG. 1A is a high level block diagram illustrating further
details relating to components within the massive MIMO wireless
communication system of FIG. 1. The wireless communication system
component portions 150 collectively depicted in FIG. 1A is a
portion of the wireless network 100 of FIG. 1. As understood by
those skilled in the art, each BS 101-103 and each MS 111-116
includes an array of antenna or antenna elements, a transmitter and
a receiver each separately coupled to the antenna to transmit or
receive radio frequency signals, encoding and modulation circuitry
within the transmitter chain coupled to the transmitter and
demodulation and decoding circuitry within the receiver chain
coupled to the receiver, and a programmable processor or controller
including and/or connected to memory and coupled to the transmitter
and receiver chains for controlling operation of the respective BS
or MS.
[0034] In the example of FIG. 1A, wireless communication is
effected by at least one radio frequency (RF) transmitter chain 151
coupled to an array of antenna or antenna elements 152 and
controlled by a processor (not shown) and at least one RF receiver
chain 153 coupled to an array of antenna or antenna elements 154
and also controlled by a processor (also not shown). In the
exemplary embodiment, the transmitter chain 151 forms part of one
of BSs 101-103 and the receiver chain 153 forms part of one of the
MSs 111-116 in the exemplary embodiment. However, as understood by
those skilled in the art, each BS 101-103 and each MS 111-116
includes both a transmitter and a receiver each separately coupled
to the respective antenna array to transmit or receive radio
frequency signals over the channel therebetween, such that the
transmitter chain 151 may alternatively be disposed within one of
the MSs 111-116 and the receiver chain 152 may alternatively be
disposed within one of the BSs 101-103.
[0035] It should be noted that each BS 101-103 and each MS 111-116
may have multiple instances of duplicative RF transmitter and
receiver chains 151 and 153 each coupled to one or more
processor(s) operating cooperatively and each separately processing
signals for transmission on antenna array 152 or signals received
on antenna array 154. Four transmitter and receiver chains are
depicted in FIG. 1A, although a given communications device (one of
BSs 101-103 or MSs 111-116) may have either more or fewer such RF
chains. The presence of multiple RF chains may be exploited in
connection with the present disclosure in the manner discussed in
further detail below.
[0036] In the example depicted, the transmitter chain 151 includes
encoding and modulation circuitry comprising channel encoder 155
receiving and encoding data for transmission, an interleaver 156
coupled to the channel encoder 155, a modulator 157 coupled to the
interleaver 156, and a demultiplexer 158 coupled to the modulator
157 and antenna elements 152. In the example depicted, the receiver
chain 153 includes demodulation and decoding circuitry and
comprising a demodulator 159 coupled to the antenna elements 154, a
deinterleaver 160 coupled to the demodulator 159 and a channel
decoder 161 coupled to the deinterleaver 160. In addition,
transmitter chain 151 and receiver chain 152 may each be coupled to
or include a programmable processor or controller (not shown)
including and/or connected to memory (also not shown) and
controlling operation of the respective BS or MS. Using such
components, synchronization signals are transmitted by a BS and
received by an MS in the manner described in further detail
below.
[0037] FIG. 2 diagrammatically illustrates some spatial processing
technologies that may be employed during hierarchical channel
sounding and channel state information feedback within a massive
MIMO wireless network according to one or more embodiments of the
present disclosure. In the example shown in FIG. 2, the cell 201
has three sectors each covering 120.degree. of the azimuth, with
four 30.degree. slices within each sector, where a "slice" is
defined as the coverage area of a set of transmitter spatial
processing schemes within a sector. In MIMO systems with large
number of antennas, Tx BF and Rx BF are frequently used to improve
desired signal strength and reduce unwanted interference. Both the
base station and the mobile station can use BF, with different
half-power beam widths (HPBWs). For example, for a base station to
transmit a control channel message to UEs in a slice, a coarse Tx
BF precoder with 30.degree. HPBW can be used so that the resulting
transmission covers the whole slice 202a. For a base station to
transmit to a particular mobile station, a fine Tx BF precoder with
smaller HPBW can be used for increased BF gain and reduced
interference to other UEs.
[0038] Coarse Tx BF has many benefits. Signals 202a, 202b, 202c,
202d, 202e and 202f precoded using coarse Tx BF precoders are easy
to acquire with only a small amount of reference signal overhead.
Once identified, the base station can use the respective coarse Tx
BF precoder to communicate to a mobile station within the coverage
area (preferably a portion of a slice) for a long period of time,
since the coverage of a coarse Tx BF precoder signal is generally
wide and generally a mobile station takes a long time to move out
of the coverage are of a coarse Tx BF precoder signal. However, due
to the large HPBW, coarse Tx BF has small Tx BF gain, which means a
reduced link budget or data rate and increased interference to
other users, slices or sectors. For such reasons, it is generally
preferred to use coarse Tx BF precoders for system broadcast,
control channel transmission, and data channel communication to
high mobility users.
[0039] On the other hand, signals 203a, 203b, 203c and 203d
precoded using fine Tx BF precoders have large Tx BF gain and can
thus increase the desired signal strength and reduce interference
significantly, which leads to user throughput and system capacity
improvement. However, sophisticated channel state information (CSI)
acquisition procedures with extensive reference signal overhead are
required to obtain the necessary channel state information for
accurate selection or generation of fine Tx BF precoders. Fine Tx
BF precoders are also sensitive to channel estimation error and,
due to the small HPBW, communications over these precoders are
subject to frequent switching since mobile stations easily move out
of the coverage of a fine Tx BF precoder. In some situations, even
the short-term, small-scale fading (i.e., fast fading) of the
channel can cause fine Tx BF precoder change. For such reasons,
fine Tx BF precoders are generally preferred for use in data
channel communication to low mobility users where closed-loop BF
can be established.
[0040] Similarly, coarse Rx BF reception patterns 204a, 204b and
204c and fine Rx BF reception patterns 205a and 205b can be
employed at the mobile station side, depending on the channel
condition, the signals or channels to be carried, and mobility.
[0041] In the illustration of FIG. 2, coarse Tx BF, fine Tx BF,
coarse Rx BF, and fine Rx BF are described and analyzed for the
downlink. Similar analysis can be obtained for coarse and fine Tx
and Rx BF in the uplink. In addition, there can also be multiple
levels of coarse and fine precoders for Tx and Rx BF.
[0042] With hierarchical channel sounding and channel state
information feedback schemes, the channel state information in a
large dimensional channel matrix can be acquired and reported via
multiple stages with the initial stages focusing on sounding and
feedback of long-term, large-scale CSI and the latter stages
focusing on sounding and feedback of short-term, small-scale CSI.
Once the long-term and large-scale CSI is acquired, coarse Tx and
Rx BF can be established, which improves the performance of
communications for certain channels, e.g., packet data control
channels. Additionally, the CSI sounding signals (or reference
signals) and the codebook for short-term and small-scale CSI can be
dependent on the long-term and large-scale CSI. As shown in FIG. 2,
a different Tx BF codebook for fine Tx BF can be selected based on
the coarse Tx BF (or long-term and large-scale CSI). Different Rx
BF codebooks for fine Rx BF can be selected based on the coarse Rx
BF (or long-term and large-scale CSI).
[0043] FIG. 3 illustrates an exemplary timing for hierarchical
channel sounding and channel state information feedback within a
massive MIMO wireless network according to one embodiment of the
present disclosure. For simplicity, the hierarchical channel
sounding and CSI feedback are illustrated using examples with
two-stage CSI feedback, with the first stage corresponding to
coarse Tx and Rx BF based on long-term and large-scale CSI, and the
second stage corresponding to fine Tx and Rx BF based on short-term
and small-scale CSI. In some examples, the coarse Tx BF in the
downlink is further simplified to selecting a preferred or active
slice in a sector.
[0044] A plurality of sounding signals or reference signals are
transmitted to aid the acquisition of CSI in multiple stages. One
example is depicted in FIG. 3, which illustrates how CSI can be
acquired in the downlink of a massive MIMO system with a large
number of transmitter or receiver antennas. The signal sequence 300
begins with the base station transmitting synchronization (sync)
signals (sequence portion 301), preferably in a periodic fashion.
The mobile station acquires the sync signals from at least one base
station, and should preferably acquire time and frequency
synchronization with the at least one base station. In a multi-base
station environment, the mobile station should also identify the
most preferred base station (or base stations) for communication.
In addition, the base station and mobile station can also identify
long-term and large-scale transmitter and receiver side spatial
information, such as the angle of departure (AoD) information at
the base station and the angle of arrival (AoA) information at the
mobile station. Such spatial information is typically location and
environment dependent, and therefore does not change rapidly due to
short-term and small-scale fading.
[0045] The remaining portions of FIG. 3 will be explained in
conjunction with FIGS. 4A-4B and 5-9. FIGS. 4A and 4B illustrate
time-frequency-space multiplexing of synchronization signals in
connection with hierarchical channel sounding and channel state
information feedback within a massive MIMO wireless network
according to one embodiment of the present disclosure. In one
embodiment of the disclosure, to allow the base station and/or the
mobile station to acquire long-term large-scale spatial
information, the base station may transmit multiple sync signals,
with each sync signal being spatially processed by a different
transmitter spatial processing scheme. For example, the base
station may transmit multiple sync signals via multiple antennas,
or via multiple angle of departures, or using multiple transmitter
BF precoders. Each sync signal may carry an identification of the
associated transmitter spatial processing scheme, e.g., antenna ID,
transmitter BF precoder ID, or any kind of signature to identify
the associated sync signals. Each sync signal may also carry the
associated cell index, and the index of the time and frequency
resources on which the sync signal is transmitted. An example of
carrying the Cell Index, Time Index, Frequency Index, and Spatial
Index is shown in FIG. 4B, in which those variables are received as
inputs to selection of a sync sequence and generation of the sync
signal (block 401). In this example, these indices are carried
implicitly by selecting different sync sequences and/or generating
different sync signals for different values of the indices. These
multiple copies of sync signals can be multiplexed in different
time symbols, or different frequency subcarriers, or different
spatial directions.
[0046] One example of how base station transmits (and how mobile
station receives) sync signals is shown in FIG. 4A. As illustrated,
the base station transmits multiple sync signals in time,
frequency, and space domains. Here the space domain can be
interpreted as different antennas, or different BF precoders, or
different angles of departure, or different coverage area
("slices") within a cell or sector. For illustration purpose,
different sync signals are presumably transmitted in different
slices in a sector: Sync A, Sync B, Sync E and Sync F in Slice 0,
Sync C, Sync D, Sync G and Sync H in Slice 1, etc. For convenience,
we use the notation of (time, frequency, space) triplets to
describe the time-frequency resource allocation and the associated
spatial processing for a signal. Thus, in this example, base
station transmits Sync A using (Slot 0, Subband 0, Slice 0),
transmits Sync B using (Slot 0, Subband 1, Slice 0), transmits Sync
C using (Slot 0, Subband 0, Slice 1), transmits Sync D using (Slot
0, Subband 1, Slice 1), transmits Sync E using (Slot 1, Subband 0,
Slice 0), transmits Sync F using (Slot 1, Subband 1, Slice 0),
transmits Sync G using (Slot 1, Subband 0, Slice 1), and transmits
Sync H using (Slot 1, Subband 1, Slice 1). In order to distinguish
the sync signals from different cells (or sectors) at different
times, frequencies, or slices, the sync sequence selection or sync
signal generation can be dependent on some or all of cell index,
time index, frequency index, and spatial index, as shown in FIG.
4B. For example, to distinguish sync signals for different slices,
different sync sequences may be selected for the different slices;
and to distinguish sync signals for different cells, different sync
sequences may be selected for each cell. After the sync signals are
generated, the sync signals are mapped to the corresponding time
frequency resources (block 402) and are subject to the
corresponding spatial processing (block 403) before being
transmitted (block 404).
[0047] In another embodiment of the disclosure, the mobile station
can also attempt to receive the sync signal using different
receiver spatial processing schemes. For example, the mobile
station may attempt to receive the sync signals via multiple
receiver antennas, or via multiple angle of arrivals, or using
multiple receiver BF precoders. Upon successful detection of the
sync signals from at least one base station, the mobile station can
identify at least one preferred transmitter spatial processing
scheme (e.g., at least one preferred long-term large-scale Tx BF
precoder), and at least one preferred receiver spatial processing
scheme (e.g., at least one preferred long-term large-scale Rx BF
precoder). The identification of these preferred base stations for
a mobile station, and the associated preferred long-term
large-scale transmitter and receiver spatial processing, can
greatly help the base station and the mobile station narrow down
the space for further sounding and estimation of short-term
small-scale channel state information. At least one (long-term
large-scale BS Tx Spatial Processing, long-term large-scale MS Rx
Spatial Processing) pair can be identified as the preferred spatial
processing scheme for the link between the base station and the
mobile station. The mobile station can report the detected at least
one base station, the identified at least one preferred long-term
large-scale transmitter spatial processing, and the identified at
least one preferred long-term large-scale receiver spatial
processing back to the network. The network, which includes the at
least one preferred base station, determines at least one active
transmitter (or active slice) spatial processing scheme for
communications with the MS. Preferably, the at least one active
transmitter (or active slice) spatial processing scheme should be
selected from the Tx BF schemes of the at least one preferred (Tx
BF, Rx BF) pair that is indicated by the MS. The BS should also
signal the selected at least one active transmitter (or active
slice) spatial processing scheme to the MS, among other spatial
processing configuration parameters.
[0048] FIG. 5 illustrates one example of the BS and MS operation
for acquiring long-term large-scale channel state information via
sync signals according to one embodiment of the present disclosure.
The exemplary process 500 for acquiring long-term, large-scale
spatial CSI information using sync signals begins with the base
station(s) transmitting sync signals with multiple Tx precoders
(step 501). The MS receives the transmitted sync signals with
multiple Rx precoders (step 502), identifies the preferred Tx BF,
Rx BF pair(s) for at least one of the base stations that
transmitted sync signals (step 503), and feeds back at least one of
the identified preferred, Tx BF, Rx BF pair(s) to the at least one
preferred base station (step 504). The mobile station may identify
and feedback more than one preferred Tx BF, Rx BF pair (with an
indication of an order of preference, such as an order of listing)
for each base station that transmitted sync signals detected by the
MS, and may identify and feedback preferred Tx BF, Rx BF pair(s)
for more than one base station that transmitted sync signals
detected by the MS (again, with some indication of an order of
preference, such as an order of listing). In identifying
"preferred" Tx BF, Rx BF pair(s), the MS may employ threshold
criteria, which may differ for different base stations that
transmitted sync signals detected by the MS, or may identify only a
predetermined total number of preferred Tx BF, Rx BF pair(s),
either per base station or for all of the base stations in the
aggregate. The preferred base station(s) determine at least one
active Tx BF scheme (or active slice) for the MS (step 505), and
signal(s) the at least one active Tx BF scheme (or active slice) to
the MS (step 506).
[0049] Referring back to FIG. 3, in CSI acquisition steps
subsequent to the sequence portion 301 discussed above, the base
station selects short-term small-scale transmitter beamforming
precoders (or other transmitter spatial processing schemes) that
are strongly correlated with the long-term large-scale Tx BF
precoders determined based upon the previously transmitted signals
(e.g., sequence 301 in this example), and the mobile station
selects short-term small-scale Rx BF precoders (or other receiver
spatial process schemes) that are strongly correlated with the
long-term large-scale Rx BF precoders determined in earlier steps
(e.g., based upon sequence 301 in this example). In other words,
the reference signals, and the search space for short-term
small-scale transmitter spatial processing schemes (e.g., the
transmitter BF/SDMA/MIMO codebook), and the search space for
short-term small-scale receiver spatial processing schemes (e.g.,
the receiver BF/SDMA/MIMO codebook), and the MS feedback of the
short-term small-scale transmitter and/or receiver spatial
processing schemes, can be dependent on the long-term large-scale
transmitter and receiver spatial processing schemes determined
earlier.
[0050] In one embodiment of the disclosure, the dependency can be
manifested as choosing a different transmitter BF/SDMA/MIMO
codebook (or a different set of transmitter BF/SDMA/MIMO precoders)
for different long-term, large-scale transmitter spatial processing
schemes, when selected.
[0051] The different codebooks may be derived in many ways. For
instance, assuming that the base station and the mobile station
select a first slice as the preferred slice for the mobile station,
the base station and the mobile station can select a first codebook
as the codebook for feedback of short-term small-scale CSI. If the
base station and the mobile station alternatively select a second
slice as the preferred slice for the mobile station, the base
station and the mobile station can select a second codebook for the
second slice as the codebook for feedback of short-term small-scale
CSI. The selection of the codebook for short-term small-scale CSI
feedback can be explicitly signaled between the base station and
the mobile station. For example, the base station may send a
message to a mobile station to assign a codebook for the mobile
station to use for CSI feedback. Alternatively, a slice-to-codebook
mapping can be established in advance, such that once the preferred
slice for a mobile station is selected, both the base station and
the mobile station know what codebook should be used for short-term
small-scale CSI feedback according to the slice-to-codebook
mapping.
[0052] Similarly, the base station and the mobile station may
select a different subset in a codebook subset for different
slices, when selected. The selection of the subset can be signaled
explicitly, or can be established via a slice-to-subset mapping
established in advance.
[0053] The base station and the mobile station may choose a
different method of transformation (e.g., a transformation matrix)
for a different slice. The selection of the transformation can be
signaled explicitly, or can be established via a
slice-to-transformation mapping.
[0054] The base station and the mobile station may choose a
different method of construction for a slice or for different
slices among a plurality of slices. The selection of the codebook
construction can be signaled explicitly, or can be established via
a slice-to-construction mapping.
[0055] In another embodiment of the disclosure, the dependency can
be manifested as choosing a different receiver BF/SDMA/MIMO
codebook (or a different set of receiver BF/SDMA/MIMO precoders)
for a different long-term large-scale receiver spatial processing
scheme (e.g., determined in step 201). Like the different
transmitter codebook, the different receiver codebook can be
derived in many ways, e.g., using codebook selection, or codebook
subset selection, or codebook transformation, or codebook
construction. And the selection of the codebook, or codebook
subset, or codebook transformation, or codebook construction can be
signaled explicitly from the base station to the mobile station (or
vice versa), or be established as an implicit mapping from the
selected long-term large-scale receiver spatial processing
scheme.
[0056] In another embodiment of the disclosure, the dependency can
also be manifested as mapping an index of a MS feedback field to
different transmitter BF/SDMA/MIMO precoders for different
long-term large-scale transmitter spatial processing scheme (e.g.,
as determined based upon sequence 301). For example, if a mobile
station selects a first slice as the active slice for that mobile
station at a current location under current conditions, a first
index of a MS feedback field can be mapped to a first Tx precoder;
however if the mobile station instead selects a second slice as the
active slice, the first index of the MS feedback field can be
mapped to a second Tx precoder. The different index-to-precoder
mapping can be either signaled explicitly, or may be determined
implicitly according to the selected long-term large-scale
transmitter spatial processing scheme.
[0057] In another embodiment of the disclosure, the dependency can
also be manifested as mapping an index of a MS feedback field to
different receiver BF/SDMA/MIMO precoders for different long-term
large-scale receiver spatial processing scheme (e.g., as determined
based upon sequence 301). For example, if a mobile station selects
a first wide-beam receiver precoder as the preferred long-term
large-scale receiver precoder for that mobile station at a current
location under current conditions, a first index of a MS feedback
field can be mapped to a first Rx precoder; however if the mobile
station instead selects a second wide-beam receiver precoder as the
preferred long-term large-scale receiver precoder, the first index
of the MS feedback field can be mapped to a second Rx precoder. The
different index-to-precoder mapping can be either signaled
explicitly, or may be determined implicitly according to the
selected long-term large-scale receiver spatial processing
scheme.
[0058] FIG. 6 is a process flow diagram of an example of base
station and mobile station operation with short-term CSI feedback
depending on long-term CSI feedback according to one embodiment of
the present disclosure. In this example, the long-term large-scale
CSI is represented by the active slice of a mobile station.
Depending on which slice is active for a mobile station, the mobile
station may use different codebooks for its CSI feedback. Thus the
process 600 begins with the BS transmitting sync signals in
multiple slices (step 601), which are received in multiple slices
by the MS (step 602). The MS identifies at least one preferred
slice (step 603) and feeds back the identity of the at least one
preferred slice to the BS (step 604). Upon receiving the MS
feedback of the at least one preferred slice from the MS (step
605), the BS and MS negotiate at least one actual slice to be
active for the MS, and select the CSI feedback codebook for the MS
based on the selected at least one active slice and the MS feedback
(step 606).
[0059] Referring back to FIG. 3, the base station can transmit
sector-level common reference signals (sector-level CRS) in signal
sequence 302. These sector-level CRS can be transmitted via
multiple antennas or using multiple transmitter BF precoders. These
sector-level CRS can be multiplexed in time, frequency, and space.
Different sequences can be used for different sector-level CRS for
identification, interference randomization and suppression
purposes. As a result, sector-level CSI or sub-sector-level CSI can
be acquired using these reference signals. The base station may
broadcast certain common control signals (e.g., Broadcast Control
Channel) to the whole sector together with the sector-level CRS.
The mobile stations can use the sector-level CRS to estimate the
channel for demodulation of these common control signals. At the
same time, the mobile station receiving the sector-level CRS
signals can use these sector-level CRS to improve the accuracy and
granularity of CSI for feedback purpose. In the example shown in
FIG. 3, the mobile station utilizes the sector-level CRS to improve
the sector-level and sub-sector-level spatial CSI. If the
sector-level CRS provides sufficient coverage and density in both
time and frequency, higher resolution and accuracy of the CSI in
time and frequency (e.g., sub-band CSI feedback for closed-loop
BF/SDMA/MIMO operation) can also be obtained.
[0060] In signal sequence 302, the base station can also transmit
sector-level CSI reference signals (sector-level CSI-RS). These
sector-level CSI-RS can be transmitted via multiple antennas or
using multiple transmitter BF precoders. These sector-level CSI-RS
can be multiplexed in time, frequency, and space. Different
sequences can be used for different sector-level CSI-RS for
identification, interference randomization, and interference
suppression purposes. Compared with sector-level CRS, the
sector-level CSI-RS received by the MS primarily serve the purpose
of assisting CSI estimation at the mobile station for CSI feedback.
Therefore, the time-frequency density (and thus the overhead) of
the sector-level CSI-RS can be made lower than that of the
sector-level CRS. On the other hand, in order to improve the
spatial resolution of the sector-level CSI-RS in a MIMO system with
large number of transmitter and receiver antennas, the sector-level
CSI-RS may provide higher spatial sounding capability than the
sector-level CRS. For example, the base station can transmit the
sector-level CSI-RS using a larger number of transmitter BF
precoders than the number of transmitter BF precoders used to
transmit sector-level CRS. In order to achieve higher spatial
sounding capability, the transmitter BF precoders for sector-level
CSI-RS should also have higher BF gain, and thus smaller half-power
beam width (HPBW), than the transmitter BF precoders for
sector-level CRS. The mobile station can use these sector-level
CSI-RS to improve the accuracy and granularity of CSI estimation
for CSI feedback. In the example shown in FIG. 3, the mobile
station utilizes the sector-level CSI-RS to improve the
sector-level and sub-sector-level spatial CSI. If the sector-level
CSI-RS provide sufficient coverage and density in both time and
frequency domain, higher resolution and accuracy of the CSI in time
and frequency (e.g., sub-band CSI feedback for closed-loop
BF/SDMA/MIMO operation) can also be obtained.
[0061] In signal sequence 303, the base station can transmit
slice-level CRS (step 607). Like the sector-level CRS, these
slice-level CRS can be transmitted via multiple antennas or using
multiple transmitter BF precoders. These slice-level CRS can be
multiplexed in time, frequency, and space. Different sequences can
be used for different slice-level CRS for identification,
interference randomization, and interference suppression purposes.
As a result, slice-level CSI or sub-slice level CSI can be acquired
using these reference signals (step 608). Once the BS receives CSI
feedback from the MS (step 610), the BS transmits scheduling grants
and data packets to the MS based on the feedback (steps 611 and
612). Different from the sector-level CRS, the slice-level CRS of a
slice are transmitted using transmitter BF precoders that have
strong spatial correlation with the slice. In other words, the
slice-level CRS of a slice stay "within" or "close to" the spatial
coverage of a slice in a sector. As such, the interference between
a first slice-level CRS in a first slice of a sector and a second
slice-level CRS in a second slice of that sector is likely to be
small.
[0062] In one embodiment of the disclosure, a base station can
spatially multiplex the slice-level CRS of different slices in the
same time and frequency resources. Different sequences should be
used for these reference signals to achieve identification,
interference randomization, and interference suppression. The base
station may broadcast certain common control signals (e.g., Packet
Data Control Channel) to the whole slice together with the
slice-level CRS. The mobile stations can use the slice-level CRS to
estimate the channel for demodulation of these common control
signals. At the same time, the mobile station can use these
slice-level CRS to improve the accuracy and granularity of CSI for
feedback purpose (step 608). In the example shown in FIG. 3, the
mobile station utilizes the slice-level CRS to improve the
slice-level and sub-slice-level spatial CSI. If the slice-level CRS
provides sufficient coverage and density in both time and
frequency, higher resolution and accuracy of the CSI in time and
frequency (e.g., sub-band CSI feedback for closed-loop BF/SDMA/MIMO
operation) can also be obtained.
[0063] In another embodiment of the disclosure, the configuration
of slice-level CRS can be dynamically adjusted. For example, base
station may turn off the slice-level CRS of a slice if there is no
mobile station in connected state currently located in that slice.
The base station may subsequently turn on the slice-level CRS of a
slice if at least one mobile station in the connected state enters
into that slice. More generally, the base station can dynamically
configure the density of slice-level CRS of a slice depending on
the load in that slice. Upon reconfiguring the slice-level CRS, the
base station should transmit a message to the mobile stations in
the slice to inform those mobile stations of the change. The
message can be either a broadcast message or a uni-cast message.
Upon receiving the message of slice-level CRS configuration, each
mobile station should reconfigure its CSI channel estimator to
utilize the new configuration of slice-level CRS for CSI channel
estimation purposes.
[0064] In signal sequence 303, the base station can also transmit
slice-level CSI-RS (also step 607). Like the sector-level CSI-RS,
these slice-level CSI-RS can be transmitted via multiple antennas
or using multiple transmitter BF precoders. These slice-level
CSI-RS can be multiplexed in time, frequency, and space. Different
sequences can be used for different slice-level CSI-RS for
identification, interference randomization and interference
suppression purposes. As a result, slice-level CSI or sub-slice
level CSI can be acquired using these reference signals (step
608).
[0065] In one embodiment of the disclosure, the slice-level CSI-RS
of a slice are transmitted using transmitter BF precoders that have
strong spatial correlation with the slice. In other words, the
slice-level CSI-RS of a slice stay "within" or "close to" the
spatial coverage of a slice in a sector. As such, the interference
between a first slice-level CSI-RS in a first slice of a sector and
a second slice-level CSI-RS in a second slice of that sector is
likely to be small.
[0066] In another embodiment of the disclosure, a base station
spatially multiplexes the slice-level CSI-RS of different slices in
the same time and frequency resources. The base station may use
different sequences for the slice-level CSI-RS in different slices
to achieve identification, interference randomization, and
interference suppression.
[0067] In another embodiment of the disclosure, the configuration
of slice-level CSI-RS can be dynamically adjusted. For example,
base station may turn off the slice-level CSI-RS of a slice if
there is no mobile station in a connected state currently located
within that slice. The base station may subsequently turn on the
slice-level CSI-RS of a slice if at least one mobile station in a
connected state enters into that slice. More generally, the base
station can dynamically configure the density of slice-level CSI-RS
of a slice depending on the load in that slice. Upon reconfiguring
the slice-level CSI-RS, the base station should transmit a message
to the mobile stations in the slice to inform those mobile stations
of the changes. The message can be either a broadcast message or a
uni-cast message. Upon receiving the message of slice-level CSI-RS
configuration, the mobile station should reconfigure its CSI
channel estimator to utilize the new configuration of slice-level
CSI-RS for CSI channel estimation purpose.
[0068] FIG. 7 is a process flow diagram of an example of channel
sounding and CSI feedback with configurable slice-level CSI-RS (or
CRS) according to one embodiment of the present disclosure. Steps
701 through 704 of the process 700 are substantially identical in
purpose and effect to steps 601 through 605 of process 600
illustrated in FIG. 6, and steps 708 through 713 are substantially
identical in purpose and effect to steps 607 through 612. In
process 700, however, after long-term large-scale CSI is acquired,
a codebook for short-term small-scale feedback is determined as
part of the selection of an active slice for the MS (step 705). In
addition, the configuration and transmission of slice-level CSI-RS
(or CRS) also depends on the long-term large-scale CSI. The BS may
turn on, or turn off, or change the configuration of slice-level
CSI-RS (or CRS), and communicates this change to the intended MS
(steps 706 and 707). By doing so, the BS can allow the MS to use
more CSI-RS (or CRS) for better CSI estimation when needed, while
at the same time limiting the overhead of CSI-RS (or CRS) by
turning off transmission of such signals or by reducing the density
when those signals are not needed.
[0069] Compared with slice-level CRS, the slice-level CSI-RS
primarily serves the purpose of assisting CSI estimation at the
mobile station for CSI feedback purpose (step 709). Therefore, the
time-frequency density (and thus the overhead) of the slice-level
CSI-RS can be made lower than that of the slice-level CRS. On the
other hand, in order to improve the spatial resolution of the
slice-level CSI-RS in a MIMO system with large number of
transmitter and receiver antennas, the slice-level CSI-RS may
provide higher spatial sounding capability than the slice-level
CRS. For example, the base station can transmit the slice-level
CSI-RS using a larger number of transmitter BF precoders than the
number of transmitter BF precoders used to transmit slice-level
CRS. In order to achieve higher spatial sounding capability, the
transmitter BF precoders for slice-level CSI-RS should also have
higher BF gain, and thus smaller half-power beam width (HPBW), than
the transmitter BF precoders for slice-level CRS. The mobile
station can use these slice-level CSI-RS to improve the accuracy
and granularity of CSI estimation for CSI feedback. In the example
shown in FIG. 3, the mobile station utilizes the slice-level CSI-RS
to improve the slice-level and sub-slice-level spatial CSI. If the
slice-level CSI-RS provide sufficient coverage and density in both
time and frequency domain, higher resolution and accuracy of the
CSI in time and frequency (e.g., sub-band CSI feedback for
closed-loop BF/SDMA/MIMO operation) can also be obtained.
[0070] FIG. 8 is an example of slice-level CSI-RS transmission for
use in channel sounding and CSI feedback with configurable
slice-level CSI-RS (or CRS) according to one embodiment of the
present disclosure. In this example, there are four slices, S0, S1,
S2, and S3, within the sector. A first codebook with four beams,
B0, B1, B2, and B3, is used for the slice-level CSI-RS transmission
in slice S0; a second codebook with four beams, B4, B5, B6, and B7,
is used for the slice-level CSI-RS transmission in slice S1; a
third codebook with four beams, B8, B9, B10, and B11, is used for
the slice-level CSI-RS transmission in slice S2; and a fourth
codebook with four beams, B12, B13, B14, and B15, is used for the
slice-level CSI-RS transmission in slice S3. Note these beams, B0
through B15, can be subsets of a larger codebook, and that such
subsets may have overlap, i.e., having one or multiple common or
overlapped beams.
[0071] The slice-level CSI-RS transmission is also shown in FIG. 8.
In each slice S0 through S3, slice-level CSI-RS can be transmitted
in different time-frequency resources using different beams. For
example, in slice S0, slice-level CSI-RS is transmitted using B0 in
resources with (time, frequency) indices of (0, 0), (0, 4), (4, 2),
and (4, 6), and is also transmitted using B1 in resources with
(time, frequency) indices of (0,1), (0,5), (4,3), and (4,7), and is
additionally transmitted using B2 in resources with (time,
frequency) indices of (0,2), (0,6), (4,0), and (4,4), and still
further is transmitted using B3 in resources with (time, frequency)
indices of (0,3), (0,7), (4,1), and (4,5). These transmissions
allow sufficient sounding of the channel in each beam on the whole
time-frequency space. As also as shown in FIG. 8, similar
transmission schemes can be used in other slices as well.
[0072] SDMA can be used for slice-level CSI-RS transmission, i.e.,
slice-level CSI-RS on two different beams can be transmitted in the
same time-frequency resources. For example, as shown in FIG. 8,
CSI-RS for B0 and CSI-RS for B8 are transmitted in different slices
(S0, S2) using the same set of resources with (time, frequency)
indices of (0,0), (0,4), (4,2), and (4,6). Similarly, CSI-RS for B1
and CSI-RS for B9 are transmitted in those slices using the same
set of time-frequency resources, while CSI-RS for B2 and CSI-RS for
B10 are transmitted in the same set of time-frequency resources,
etc. In like manner, CSI-RS for B7 and CSI-RS for B15 (for example)
are transmitted in different slices (S1, S3) using the same set of
time-frequency resources. The CSI-RS for different beams that are
transmitted on the same time-frequency resources should be
carefully chosen such that inter-beam interference is minimized.
Additionally, different scrambling sequences or spreading sequences
can be used for each beam such that inter-beam interference can be
further suppressed.
[0073] Again referring back to FIG. 3, in signal sequence 304, the
base station transmits MS-specific demodulation reference signals
(DMRS) to assist mobile station demodulation of data channel
transmissions. The base station generally only allocates a portion
of the time frequency resources for a data channel transmission to
a mobile station. The DMRS signals, which assist the mobile station
in demodulation of the data channel transmissions, should therefore
only be transmitted within the allocated time frequency resources
for the respective mobile station. The DMRS signals are used to
acquire CSI for demodulation within the reduced CSI space as a
result of acquiring the long-term and large-scale CSI. Note that
even within this reduced CSI space, there can still be multiple
degrees of freedom in the spatial domain. In other words, MIMO
transmission with rank greater than 1, i.e., multi-layer MIMO
transmission, can still occur. As such, there can also be multiple
layers of DMRS signals. The multiple layers of DMRS signals and the
multiple layers of data channel transmissions can go through the
same spatial processing. In this case, the mobile station can
acquire the CSI needed for data channel demodulation by estimating
the channel coefficients directly from the DMRS signals.
Alternatively, additional precoding can be applied to transform
from the precoder of the DMRS signals to the precoder of the data
channel MIMO transmissions. In this case, the base station needs to
explicitly signal the additional precoding to the mobile
station.
[0074] In signal sequence 304, the base station also transmits
MS-specific CSI-RS. Like the slice-level CSI-RS, these MS-specific
CSI-RS signals can be transmitted via multiple antennas or using
multiple transmitter BF precoders. These MS-specific CSI-RS signals
can be multiplexed in time, frequency, and space. Different
sequences can be used for different MS-specific CSI-RS for
identification, interference randomization, and interference
suppression purposes.
[0075] In one embodiment of the disclosure, the MS-specific CSI-RS
for a mobile station are transmitted using transmitter BF precoders
that have strong spatial correlation with the channel from the base
station to the mobile station. In other words, the MS-specific
CSI-RS of a MS stay "within" or "close to" the channel from the BS
to the MS. Like slice-level CSI-RS, a base station can spatially
multiplex the MS-specific CSI-RS of different mobile stations in
the same time and frequency resources. The configuration of
MS-specific CSI-RS can be dynamically adjusted. For example, base
station may turn off the MS-specific CSI-RS if there is no need for
the MS to measure CSI using the MS-specific CSI-RS. The base
station may turn on the MS-specific CSI-RS for a mobile station if
there is a need for that MS to measure CSI using the MS-specific
CSI-RS. More generally, the base station can dynamically configure
the density of MS-specific CSI-RS for a mobile station. Upon
reconfiguring the MS-specific CSI-RS, the base station should
transmit a message to the mobile station to inform the mobile
station of the reconfiguration. The message can be either a
broadcast message or a uni-cast message. The BS can send the
MS-specific CSI-RS configuration information together with a
request for the MS to feedback CSI measured from the MS-specific
CSI-RS.
[0076] FIG. 9 is a process flow diagram for one example of
MS-specific CSI-RS transmission and the associated CSI feedback
according to one embodiment of the present disclosure. In the
process 900 of this example, the base station initiates the
transmission of MS-specific CSI-RS (step 901), which is received by
the MS (step 902). The base station can send a request to mobile
station for CSI feedback (step 903). Preferably at the same time of
the request, the base station configures MS-specific CSI-RS to
assist the MS in CSI feedback, and transmits that MS-specific
CSI-RS to the MS (step 905). Upon receiving the CSI feedback
request (step 904) and the configuration of MS-specific CSI-RS
(step 906), the mobile station knows the resource allocation for
the MS-specific CSI-RS and can thus use that resource allocation
for CSI feedback (step 907). Steps 908 through 910 of the process
900 are substantially identical in purpose and effect to steps 610
through 612 of process 600 illustrated in FIG. 6.
[0077] Notably, the CSI feedback request can also be made implicit.
For example, if mobile station detects the message that carries a
valid MS-specific CSI-RS configuration, the valid MS-specific
CSI-RS configuration can be used as an indication that the BS is
requesting a CSI feedback. The configuration of MS-specific CSI-RS
can be valid for only one transmission, or multiple transmissions,
or periodic, or remain valid until the next configuration.
[0078] FIG. 10 is a process flow diagram for another example of
MS-specific CSI-RS transmission and the associated CSI feedback
according to one embodiment of the present disclosure. In this
process example 1000, the mobile station requests the transmission
of MS-specific CSI-RS from the base station (steps 1001 and 1002).
If the request is allowed by the base station, the base station
configures MS-specific CSI-RS to assist the MS in CSI feedback, and
transmits the configuration (step 1003). Upon receiving the
configuration of MS-specific CSI-RS (step 1004), the mobile station
knows the resource allocation for the MS-specific CSI-RS and can
thus use that resource allocation for CSI feedback (step 1007).
Steps 1008 through 1010 of the process 1000 are substantially
identical in purpose and effect to steps 610 through 612 of process
600 illustrated in FIG. 6.
[0079] In summary, using the sync and reference signals transmitted
in sequences 301 and 302 of FIG. 3, the mobile station should be
able to identify the long-term large-scale CSI with good fidelity.
The selection of preferred sectors and preferred slices also
reduces the channel state information space in which short-term and
small-scale CSI remains to be resolved, with finer granularity and
accuracy. This reduction of channel state information space by
resolving long-term and large-scale CSI makes it practically
possible to estimate short-term and small-scale CSI within a small
channel state information space using reasonable amount of
reference signals in sequences 303 304.
[0080] FIG. 11 is an alternative illustration of the hierarchical
CSI acquisition depicted in FIG. 3. Different reference signals are
utilized in each step to achieve different level of CSI
acquisition. As the mobile station goes through the multiple CSI
acquisition steps, finer and finer granularity of CSI acquisition
is achieved.
[0081] Note that although an extensive procedure is described for
illustration purpose as shown in FIG. 3, not all reference signals
or CSI acquisition steps are needed for all systems. In some
systems or scenarios, certain steps may be skipped.
[0082] FIG. 12 depicts one example of a simplified hierarchical
channel sounding and CSI estimation scheme hierarchical channel
sounding and CSI estimation scheme according to one embodiment of
the present disclosure. In this exemplary simplified signal
sequence 1200, sync signals 1201 are transmitted as in FIG. 3 and
CRS and CSI-RS 1202 are likewise transmitted at the sector-level as
in FIG. 3, while MS-specific DMRS 1203 are used for demodulation as
in FIG. 3. Upon acquiring the coarse (long-term) transmitter and
receiver BF information, however, the MS can use sector-level
CSI-RS 1202 to estimate fine (short-term) CSI information and
generate CSI feedback directly. The codebook used by the MS for CSI
feedback depends on the coarse transmitter and receiver BF
information acquired based on sync signals 1201. This simplified
scheme 1200 will help reduce the CSI feedback overhead and improve
the CSI feedback granularity.
[0083] Although downlink CSI acquisition was used an example to
illustrate hierarchical channel sounding and CSI estimation in FIG.
3, the techniques are equally applicable in the uplink. FIG. 13
depicts an example of hierarchical uplink channel sounding and CSI
estimation according to one embodiment of the present disclosure.
As evident from comparison with FIG. 3, the signal sequence 1300 of
FIG. 13 follows similar steps as the example of a hierarchical
downlink channel sounding and CSI estimation signal sequence 300
described above, except that a Random Access Channel (RACH) uplink
transmission by the MS may occur concurrent with the transmission
of sync signals 1301, the MS-specific UL DMRS 1304 is transmitted
by mobile station instead of the MS-specific DL DMRS transmitted by
base station, and mobile station also transmits the MS-specific UL
sounding reference signal (SRS) 1304 in place of the MS-specific
CSI-RS. The signal sequences 1302-1303 parallel the counterpart
signal sequences 302-303 in FIG. 3. This scheme 1300 works well if
downlink-uplink channel reciprocity can be assumed, at least for
long-term large-scale channel state information, since the
long-term large-scale CSI is resolved using downlink reference
signals 1301-1302, while short-term small-scale CSI is resolved
using uplink reference signals 1303-1304.
[0084] FIG. 14 depicts another example of a hierarchical uplink CSI
acquisition scheme according to one embodiment of the present
disclosure. In the signal sequence 1400 of this example,
downlink-uplink channel reciprocity is not assumed. Time and
frequency synchronization and serving sector identification are
achieved via detection of sync signals 1401. Upon completing the
random access procedure (RACH), the sequence timing advances to
uplink transmissions, and coarse transmitter and receiver BF can
also be achieved for uplink transmissions. The MS transmits UL DMRS
1402 to assist the BS demodulation of uplink data channel
transmissions. The MS-specific UL SRS 1403 is transmitted for the
BS to acquire CSI for uplink scheduling. Since coarse transmitter
and receiver BF information is acquired based on the signals 1401,
the CSI space for CSI estimation based on 1402 and 1403 is reduced,
reducing the reference signal overhead needed to achieve accurate
CSI for demodulation and scheduling purpose.
[0085] While each process flow and signal sequence depicted in the
figures and described above depicts a sequence of steps and/or
signals, either in series or in tandem, unless explicitly stated or
otherwise self-evident (e.g., a signal cannot be received before
being transmitted) no inference should be drawn from that sequence
regarding specific order of performance, performance of steps or
portions or transmission of signals thereof serially rather than
concurrently or in an overlapping manner, or performance the steps
or transmission of signals depicted exclusively without the
occurrence of intervening or intermediate steps or signals.
Moreover, those skilled in the art will recognize that complete
processes and signal sequences are not illustrated or described.
Instead, for simplicity and clarity, only so much of the respective
processes and signal sequences as is unique to the present
disclosure or necessary for an understanding of the present
disclosure is depicted and described.
[0086] Although the present disclosure has been described with
exemplary embodiments, various changes and modifications may be
suggested to one skilled in the art. It is intended that the
present disclosure encompass such changes and modifications as fall
within the scope of the appended claims.
* * * * *